Movements of water and ions in mitochondria

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Abstract
Investigations were made of the conditions in which respiring rat-liver mitochondria can swell and contract in solutions of constant osmotic pressure. An essentially continuous estimation of mitochondrial water was obtained from measurements of the optical density of suspensions at 950 m[mu], with a 1 mm light path. When suspensions of rat-liver mitochondria are shaken in air at 35[degree] with 20 m[image] sodium succinate, 10 m[image] potassium phosphate buffer, pH 7.4, 5m[image] magnesium sulfate, 30 m[image] tris buffer, 83 m[image] sucrose and m[image] ATP or ADP, the rate of oxygen uptake is high (Qo2 approximately - 40 [mu]l/mg dry weight/ hour) and the particles retain their initially low water content (20-25% dry weight). In the absence of adenosine phosphates the O2 uptake is essentially unchanged in the first 30 minutes, but the mitochondria take up water (15% dry weight and the Na and K concentrations decrease. If swelling has not proceeded too far, the subsequent addition of m[image] AMP or ATP alone, or, much better, together with m[image] dinitrophenol (DNP), will cause the extrusion of water (17-21% dry weight) and partial recovery of the Na and K gradients. The time courses of these processes are not identical. This recovery is coincident with the resumption of oxidative phosphorylation and is abolished by 10-4 [image] DNP. These results indicate that "high-energy" phosphate esters can be used by mitochondria to move water and ions.
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